Wafer handler robot is in bad shape.
It collides with wafer at send cassette, pushing cassette back until it slides underneath to pick up wafer.
When taking wafer out of chamber, robot goes to wrong position, so wafer is far off center. As a result, it drops the wafer off the pins at the cooling chamber.
When putting wafers near the top of the receive cassette, the robot loads the wafers off center, so the cassette has to torque to accommodate the incoming wafer.